Checking apparatus for condition responsive system



p 21, 1965 P. GlUFFRlDA ETAL 3,208,060

CHECKING APPARATUS FOR CONDITION RESPONSIVESYSTEM Filed July 25 1963 16Fifi FIG.|

FIG.3

START (PB. 6)

United States Patent CIECKING APPARATUS FOR CONDITION RESPONSIVE SYSTEMPhilip Giuifrida, North Andover, and Donald L. Graves, Woburn, Mass,assignors to Electronics Corporation of America, Cambridge, lWass, acorporation of Massachusetts Filed July 25, 1963, Ser. No. 297,639Claims. (Cl. 340214) This invention relates to control apparatus andmore particularly to condition responsive apparatus such as those usefulin supervising fuel burning systems, and to means for insuring reliableoperation of the sensory and signal modifying portions of suchapparatus.

In condition responsive systems, as for example those used forsupervision of combustion established in a furnace chamber, it isdesirable that the system react very quickly to the presence or absenceof a flame so that excessive amounts of unburned fuel will notaccumulate in the chamber in the absence of flames. Electronic flamesensing systems have the desirable rapid reaction to presence or absenceof flame, but such systems are susceptible to malfunctions such as, forexample, a continuously avalanching sensor of the gas-discharge typewhich falsely indicates flame presence or a runaway transistor whichcontinuously passes substantial current to a flame responsive device inthe absence of the flame signal normally required to initiate andsustain such current flow. Should such a failure occur, it would be anunsafe type as the sensing system would, in the event of flame failure,continue to react as if flame were present and would therefore permitcontinued fuel introduction. In such a case the chamber can accumulatean excessive charge of fuel or fuel vapor which might be ignitedexplosively by the hot refractory or upon an attempt to reignite theburner. If the sensing system through component failure erroneouslyindicates the absence of flame, however, fuel introduction will beterminated and the failure is of a safe type.

In order to check the integrity of such condition responsive systems, ithas been proposed to employ a condition absence simulator which operatesrepetitively at intervals shorter than the deactuation time of the loadcontrol device. Failure of the condition responsive device to reactproperly to the simulated condition absence results in deactivation ofthe controlled loads. A major disadvantage of this system is the limitedlife of those mechanical portions thereof which, because of the rapidrepetition rate, amass a large number of operations within a relativelyshort period of time.

Another proposal has been to utilize a timing motor to periodicallyinitiate a condition absence simulation, with the interval between suchsimulations being appreciably longer than the response time of the loadcontrol device. Whereas the less frequent operation of the checkingapparatus contributes to its longer life expectancy, there is noassurance against malfunctions of the checking ap paratus itself, andwhen such occur there is no continuing check on the integrity of thecondition responsive system.

Accordingly, it is an object of this invention to provide novel andimproved control apparatus for checking con dition responsive systems.

Another object of the invention is to provide novel and improved controlapparatus for use with condition responsive systems which incorporatemeans to periodically simulate the absence of the condition being sensedand means to check the continued operation of the condition absencesimulator.

Another object of this invention is to provide a selfchecking conditionresponsive system in which the check- 3,208,060 Patented Sept. 21, 1965ice ing events are provided at intervals substantially longer than thepredetermined delay provided in the system between loss of the sensedcondition and operation of load devices in response to such loss.

Another object of the invention is to provide a simplified checkingsystem for a condition responsive system in which the checkingcomponents alternate between a first position and a second position andreturn to the first position only once during each checking cycle, whichcycle is substantially longer than the system delay provided between theloss of sensed condition and operation of load devices in response tosuch loss.

A further object of the invention is to provide a simplified controlcircuit particularly useful in combustion supervision systems in whichthe condition sensor will shut down the circuit in substantiallyimmediate response to the sensing of the absence of the condition, andin which the operation of the condition sensor is checked at frequentand regular intervals, the sensor and the checking circuitry beinginterconnected so that they actu ate each other automatically.

Still another object of the invention is to provide a novel and improvedflame detection control circuit which utilizes inexpensive and reliablecomponents which may be manufactured in a compact unit including meansfor regularly simulating a flame failure condition and means to checkthe operation of that simulator.

Other objects, features and advantages of the invention will be seen asthe following description of a preferred embodiment thereof progresses,in conjunction with the drawing, in which:

FIG. 1 is a schematic diagram of control circuitry constructed inaccordance with the invention employed in a combustion supervisionarrangement;

FIG. 2 is a diagrammatic view of mounting of thermally actuated timedelay relay employed in the preferred embodiment of the invention; and

FIG. 3 is a timing diagram indicating the operating sequence ofcomponents in the control circuitry of FIG. 1.

\Vith reference to FIG. 1, a volt 60 cycle power source is applied atterminals 10, 12 of the control circuitry. Connected in parallel betweenterminal 10 and line 14 is a normally open, momentarily operated pushbutton 16 and holding contacts 181 of load control relay 18. The loadcontrol relay 18 is connected between lines 14 and 20 through diode 22,normally open timer relay switch contacts 241 and normally opencondition indicating relay contacts 26-1.

Condition source 28 is shown connected between the lines 14 and 20. Thissource may be completely independent of the control circuit or acontrolled source that is initially energized by the push button control16 and may, for example, be the flame in the combustion chamber of aburner installation. Disposed adjacent source 28 is a condition sensor30 which may be a photocell sensing visible radiation from the flame, aninfra red radiation sensor or a Geiger-Muller type of ultraviolet sensorresponsive to a particular frequency range of radiation from the flame,for example. This condition sensor 30 is connected across lines 14 and20 in series with diode 32 and the condition indicating (flame) relay26. Normally, signal modifying and/or amplifying circuitry is employedbetween the sensor 30 and condition indicating device 26, but suchcircuitry has been omitted to simplify the drawing.

Also connected across lines 14 and 20 is a simulator solenoid 34 whichoperates a shutter 36 for positioning between the condition source 28and the sensor 30. Solenoid 34 is controlled by normally closed timercontrolled contacts 24-2. Other types of simulators may also beemployed, the illustrated arrangement merely being one suitable type.

The actuator 38 for the switch 24, which in the preferred embodiment isa heating coil wound about two bimetallic elements of the type shown inFIG. 2, is connected through normally closed contacts 26-2 operated bythe condition indicating relay 26 across lines 14 and 20. Finally, alsoconnected across lines 14 and in series with normally open contacts 18-2of load control relay 18 is a load generally indicated at 40 which maybe a solenoid controlled fuel valve, for example, in a combustionsupervision system.

The solenoid coil of relay 26 has a capacitor 42 connected across itwhich in combination with the impedance of the coil holds that relay induring the half cycles of line voltage blocked by diode 32, but does notsubstantially delay the drop out of the relay when an absence of thecondition to be sensed is detected. Capacitor 44, connected across thesolenoid coil of relay 18, holds that relay in for a period of threeseconds after deenergization of its coil.

The timer delay relay in the illustrated embodiment includes a miniaturemechanical switch unit 24 having normally open contacts 24-1 andnormally closed contacts 24-2. In the preferred embodiment this unit ismounted on a first bimetallic strip 46 and in spaced relation from asecond bimetallic strip 48. These strips are arranged so that they movetoward each other under the influence of heat applied by the resistanceheater element 38 wound about both of them. Improved operatingcharacteristics of this relay are obtained through this mountingarrangement. This relay has an operating cycle of about one minute,which is initiated when the control circuit is energized and relay 26 isdeenergized. Heat from the heater 38 causes the bimetal elements 46, 48to move toward one another to operate switch 24, opening contacts 24-2and closing contacts 24-1. When the heater 38 is de-energized a timingcycle is started and as the bimetal elements cool, they move apart andultimately release the switch 24, normally in about one minute. Othertiming devices, such as slow drop out relays having similar operatingcycles, may also be used.

In operation the control circuit is initially energized by depressingpush button 16 which applies electrical power to line 14. This energizesthe condition source 28 (when connected as shown in FIG. 1), simulatorsolenoid 34 and heater 38. As soon as heater 38 has brought strips 46,48 toward one another to operate switch 24, contacts 24-1 close andcontacts 24-2 open, the latter de-energizing simulator solenoid 34. Withthe withdrawal of shutter 36, detector 30 can view the flame or othercondition from source 28 and will energize the condition indicatingrelay 26, closing contacts 26-1 and opening contacts 26-2. The openingof contacts 26-2 dc-energizes thermal element 38 and the strips 46, 48

start to cool. Load control relay 18 is energized with the closing ofcontacts 26-1 (switch contacts 24-1 already being closed) to closeholding contacts 18-1 and load contacts 18-2.

The system now continuously senses flame or other condition from source28 and should the sensor 38 detect absence of the condition, solenoid 26will promptly be .de-energized and open contacts 26-1, de-energizing thesolenoid of load control relay 18 so that relay drops out in the threeseconds time delay. With the drop out of relay 18 the load 40 isde-energized, and the holding contacts 18-1 are opened, de-energizingthe entire control circuit.

Should no condition failure be detected, as is the usual case in acombustion supervision system, the bimetal elements 46, 48 graduallycool until they have moved apart sufficiently for the contacts 24-1 and24-2 to return to their original states as shown in FIG. 1,de-energizing the load relay circuit and energizing the solenoid 34 tointerpose shutter 36 between the sensor 30 and source 28.

This simulated condition absence ale-energizes the condition indicatingrelay 26, opening contacts 26-1 and closing contacts 26-2.

The circuit to the load control relay 18 is opened by contacts 26-1, butat the same time current flow, applied to heater 38 through closedcontacts 26-2, moves the strips 46, 48 toward one another quickly. Assoon as the time delay relay opens contacts 24-2 solenoid 34 isde-energized. Contacts 24-1 close and condition indicating relay 26 isagain energized as soon as sensor 30 sees the flame for example so thatthe load control relay circuit is again complete with the closing ofcontacts 26-1, within a time substantially less than the drop out delayof relay 18. This cycle is repeated as determined by the cycle of thetime delay relay to regularly simulate condition absence.

If the sensor 39 or its associated signal modifying circuitry shouldfail in condition indicating condition (unsafe failure), relay 26 wouldnot drop out when the shutter 36 is positioned between the source andthe sensor at the end of a control cycle. Contacts 26-2 remain open,preventing reheating of the timer control strips 46, 48, and, sincecontacts 24-1 are open, the load control relay 18 will shortly drop outfor de-energization of the load and the checking circuit. Thus thesensor and its circuitry is checked regularly for failure. The timerrelay switch 24 operating cycle is initiated by de-energization of thetimer switch actuator (via contacts 26-2) and a cycle is completed aftera preestablished period of deenergization of the heater. Should theswitch actuator not be de-energized due to failure of solenoid 26 toopen contacts 26-2, the load control circuit remains open (crossconnected contacts 26-1) so that the load is deenergized in safecondition. In the preferred embodiment the actuator for contacts 24-1,24-2 comprises two spaced juxtaposed bimetal strips 46, 48 which controlthe opening of contacts 24-1 as the result of a cooling process. Suchprocess ensues if the bimetal heater 38 fails in a manner to discontinueheating with resulting safe deenergization of the load. The bimetalstrips employ in their action no hinge, linkage or other mechanism whichmay bind to prevent their proper action. The actuator for safety contact24-1 is thus an inherently fail-safe device.

Thus it will be seen that the invention provides a selfcheckingcondition responsive system which utilizes a minimal number ofcomponents in a simple, economical and yet reliable arrangement. Thecircuit automatically checks itself regularly with minimum mechanicalwear on its components. While a preferred embodiment of the inventionhas been shown and described, various modifications thereof will beobvious to those skilled in the art, and therefore it is not intendedthat the invention be limited to the disclosed embodiment or to detailsthereof and departures may be made therefrom within the spirit and scopeof the invention as defined in the claims.

We claim:

1. A condition responsive system comprising a condition sensor,

a condition indicating device controlled by said senor to indicate thepresence or absence of the sensed condition,

a load control device controlled by said condition indicating device,said load control device having a predetermined release delay afterde-energization,

simulator means for allowing said condition indicating device to assumea first state independently of the presence or absence of the conditionbeing sensed,

a timer operative independently of the presence or absence of thecondition being sensed in a timing cycle of duration greater than therelease delay of said load control device,

electrically operated timer control means coupled to said timer forinitiating a timing cycle upon de energization of said control means,

timer responsive means to actuate said simulator means at the end ofsaid timing cycle,

means responsive to said condition indicating device in said first stateto energize said timer control means and de-energize said load controldevice,

and means responsive to the energization of said timer control means todeactuate said simulator means.

2. A condition responsive system comprising a condition sensor,

a condition indicating device controlled by said sensor to indicate thepresence or absence of the sensed condition,

a load control device controlled by said condition indieating device,said load control device having a predetermined release delay afterde-energization,

simulator means for allowing said condition indicating device to assumea first state independently of the pressence or absence of the conditionbeing sensed,

a thermally responsive timer operative independently of the presence orabsence of the condition being sensed, which provides a timing cycle ofduration greater than the release delay of said load control device, asa function of its cooling rate,

a timer responsive control element having first and sec ond operativestates,

means to apply heat to said timer to place said timer responsive controlelement in said first operative state,

means responsive to said timer responsive control element being in saidsecond state to operate said simu lator means,

means responsive to said condition indicating device in said first stateto energize said heat applying means and de-energize said load controldevice,

and means responsive to said timer responsive control element in saidfirst operative state to de-energize said heat applying means.

3. A combustion control system comprising a flame sensor,

a flame relay controlled by said flame sensor to indicate the presenceor absence of flame in the supervised combustion chamber,

a load control device controlled by said flame relay, said load controldevice having a predetermined release delay after de-energization,

simulator means for allowing said flame relay to be deenergizedindependently of the presence of flame in said combustion chamber,

a timer operative independently of the presence or absence of thecondition being sensed to provide a timing cycle of duration greaterthan the release delay of said load control device,

electrically operated timer control means coupled to said timer forcausing said timer to initiate a timing cycle,

timer responsive means to actuate said simulator means at the end ofsaid timing cycle,

means responsive to the de-energization of said flame relay tode-energize said load control device and to energize said timer controlmeans,

and means responsive to the energization of said timer control means todeactuate said simulator means and permit re-energization of said flamerelay.

4. The system as claimed in claim 3 wherein said timer control meansincludes a thermally responsive actuator,

said actuator providing said timing cycle as a function of its coolingrate.

5. A combustion control system comprising a flame sensor,

a flame relay responsive to said flame sensor,

a load control device responsive to said flame relay, said load controldevice having a predetermined release delay after de-energization,

simulator means to allow said flame relay to indicate the absence offlame,

a timer operative independently of the presence or absence of flame in atiming cycle of duration greater than the release delay of said loadcontrol device,

a time responsive simulator actuator,

said actuator adapted to actuate said simulator to allow said flamerelay to indicate the absence of flame when in a first state and adaptedto deactuate said simulator to permit the energization of said loadcontrol device when in a second state,

and means responsive to the de-energization of said flame relay to causesaid timer to initiate a timing cycle.

6. The system as claimed in claim 5 wherein said timer includes athermally responsive timing element and said actuator includes a circuitcontrolling switch responsive to said timing element,

said circuit controlling switch being connected to actuate saidsimulator when said actuator is in said first state and to energize saidload control device when said actuator is in said second state.

7. The system as claimed in claim 6 wherein said thermally responsiveelement includes two bimetallic elements disposed in juxtaposed spacedrelation and said circuit controlling switch is mounted on one of saidbimetallic elements.

8. A condition supervision system comprising a condition sensor adaptedto provide a signal indicating the presense of a supervised condition,

condition indicating means controlled by said condition sensor, saidcondition indicating means having a first state indicating the presenceof the supervised condition and a second state indicating the absence ofthe supervised condition,

a load control device having a predetermined release delay afterde-energization,

means responsive to said indicating means being in said first state toenergize said load control device,

a timer having a timing cycle of substantially greater duration thansaid release delay, said timer having a first state during each saidtiming cycle and a second state at the end of each said timing cycle,

simulator means responsive to said timer in its second state forallowing said condition indicating means to be placed in its secondstate independently of the pres ence of the supervised condition,

and means responsive to said condition indicating means being in saidsecond state for placing said timer in said first state.

9. A condition responsive system comprising means to supply energy tosaid system,

a condition sensor,

a condition indicating device controlled by said sensor to indicate thepresence or absence of a sensed condition,

a load control device connected for energization directly from saidsupply means and controlled by said condition indicating device, saidload control device having a predetermined release delay afterde-energization,

simulator means for allowing said condition indicating device to assumea first state independently of the presence or absence of the conditionbeing sensed,

a timer operative independently of the presence or absence of thecondition being sensed in a timing cycle of duration greater than therelease delay of said load control device,

timer responsive means to actuate said simulator means at the end ofeach timing cycle,

means responsive to said condition indicating device being in said firststate for causing said timer to initiate a timing cycle and tode-energize said load control device,

and means responsive to the initiation of a timing cycle to de-actuatesaid simulator means.

10. A combustion control system'comprising means to supply energy tosaid system,

a flame sensor,

a flame relay controlled by said sensor to indicate the presence orabsence of flame in a supervised combustion area,

a load control device connected for energization directly from saidsupply means and controlled by said flame .relay, said load controldevice having a predetermined release delay after de-energization,

simulator means for allowing said flame relay to assume a first stateindependently of the presence or absence of flame in the area beingsupervised,

a timer operative independently of the presence or absence of flame in atiming cycle of duration greater than the release delay of said loadcontrol device,

timer responsive means to actuate said simulator means at the end ofeach timing cycle,

means responsive to said flame relay being in said first state forcausing said timer to initiate a timing cycle and to de-energize saidload control device,

and means responsive to the initiation of a timing cycle to de-actuatesaid simulator means.

References Cited by the Examiner UNITED STATES PATENTS 2,639,418 5/53Sundstrom et al. 340- 214 2,798,214 7/57 Rowell 340214 2,939,933 6/60Manganaro et al. 200-113 NEIL C. READ, Primary Examiner.

1. A CONDITION RESPONSIVE SYSTEM COMPRISING A CONDITION SENSOR, ACONDITION INDICATING DEVICE CONTROLLED BY SAID SENOR TO INDICATE THEPRESENCE OR ABSENCE OF THE SENSED CONDITION, A LOAD CONTROL DEVICECONTROLLED BY SAID CONDITION INDICATING DEVICE, SAID LOAD CONTROL DEVICEHAVING A PREDETERMINED RELEASE DELAY AFTER DE-ENERIGIZATION, SIMULATORMEANS FOR ALLOWING SAID CONDITION INDICATING DEVICE TO ASSUME A FIRSTSTATE INDEPENDENTLY OF THE PRESENCE OR ABSENCE OF THE CONDITION BEINGSENSED, A TIMER OPERATIVE INDEPENDENTLY OF THE PRESENCE OR ABSENCE OFTHE CONDITION BEING SENSED IN A TIMING